1. Field of the Invention
The invention relates to a transistor, and more particularly to, a thin film transistor (TFT) adapted to be applied in a display panel.
2. Description of Related Art
A thin film transistor can be roughly categorized into a staggered one and a coplanar one based on the structure layout of the layers thereof. For the staggered thin film transistor, the semiconductor layer is disposed between the gate layer (or the insulation layer) and the source/drain layer thereof; for the coplanar thin film transistor, the source/drain layer is disposed the gate layer (or the insulation layer) and the semiconductor layer thereof. In addition, according to the structure layout of the source/drain layer, the structures of the thin film transistor may generally be categorized into one source/drain structure that contact holes are located at two sides of the thin film transistor and another source/drain structure that the source/drain layers distribute in an island form.
In a fabrication process of the thin film transistor, an active layer thereof is prone to be damaged by a plurality of etching solutions, and therefore, in the device fabrication, an etch stop layer (ESL) structure is mostly been used as a protection when layer etching on the semiconductor. In terms of the protection of an island form etch stop layer, the active layer is also influenced due to the island form etch stop layer during the etching. Therefore, in order to reduce a degree of influence on the active layer, recently an etch stop layer protection method by using contact holes at the two sides above the active layer to contact with the source/drain layer is developed. However, since a contact area of the source/drain layer and active layer of this structure is shrunk, a result thereof causes a reduction in device characteristics. Therefore, if a carrier mobility of the active layer can be enhanced, then the device characteristics may become effective.